Lift trucks having a three-stage lift mast

ABSTRACT

A lift truck having a three-stage lift mast comprising three mast sections, each such section including two uprights positioned at a horizontal distance from each other, has the two uprights of an outer section secured to the chassis of the truck and U-shaped with the U-openings facing each other. An intermediate and an inner section, the latter one provided with a load carriage, are telescopically displaceable in said outer section. On each upright of the intermediate section and inside the flanges of the uprights of the outer section are two vertical rows of guide rolls in the same vertical plane. The running surfaces of the rolls of the first row are outwardly in engagement with the inner side of the first flange of the upright of the outer section and the running surfaces of the rolls of the second row are outwardly in engagement with the inner side of the second flange of the same upright, whereas the running surfaces of the rolls of both rows at the same time are inwardly in engagement with the outer sides of a flange, belonging to the upright of the inner section and inserted between the two rows of rolls. The purpose is to make the horizontal extension of the mast perpendicular to the drive direction of the truck as small as possible.

United States Patent [191 Berkestad LIFT TRUCKS HAVING A THREE-STAGELIFT MAST [75] Inventor: Karl E. Berkestad, Mjolby, Sweden [73]Assignee: AB Bygg-Och Transportekronomi, Mjolby, Sweden [22] Filed: Aug.25, 1971 21 Appl. No.: 174,784

[52] US. Cl. 187/9, 187/95 [51] Int. Cl B661) 9/20 [58] Field of Search187/9, 95; 254/143 [56] References Cited UNITED STATES PATENTS 3,061,04510/1962 Gunning 187/9 Primary ExaminerEvon C. Blunk Assistant ExaminerW.Scott Carson Attorney-David Toren et al.

[57] ABSTRACT A lift truck having a three-stage lift mast comprisingFig. 2

[ Nov. 27, 1973 three mast sections, each such section including twouprights positioned at a horizontal distance from each other, has thetwo uprights of an outer section secured to the chassis of the truck andU-shaped with the U- openings facing each other. An intermediate and aninner section, the latter one provided with a load carriage, aretelescopically displaceable in said outer section. On each upright ofthe intermediate section and inside the flanges of the uprights of theouter section are inwardly in engagement with the outer sides of aflange, belonging to the upright of the inner section and insertedbetween the two rows of rolls. The purpose is to make the horizontalextension of the mast perpendicular to the drive direction of the truckas small as possible. I

2 Claims, 7 Drawing Figures sir/4.727

PMENTEUMWY ms SEEITT 1 CF 3 Fig. 2

' three-stage lift mast comprising three mast sections, each suchsection including two uprights positioned at a horizontal distance fromeach other, the two uprights I of an outer section being U-shaped withthe U-openings facing each other, said outer section being secured tothe chassis of the truck, whereas an intermediate and an inner sectionare telescopically displaceable in the outer section, said inner sectionbeing provided with a load carriage.

Such masts are relatively wide due to the fact that the uprights of thethree sections are positioned side by side, which decreases the sightforward. Furthermore the material of these sections from the point ofview of strength and rigidity is unsufficiently utilized as usually thecross section of said uprights is the same for all three sections.

It is a principal object of the present invention to make the horizontalextension of the mast perpendicular to the drive direction of the truckas small as possible and to redistribute the material between the uprights so that it is better utilized.

This and other objects and advantages of the invention will be apparentto those familiar with the art when the following description is read inconjunction with the drawings, in which:

FIG. 1 is a front view of the lift mast in a wholly extended position,

FIG. 2 is a cross-sectional view on the line II-ll in FIG. 1,

FIG. 3 is a cross-sectional view on the line III-III in FIG. 1,

FIG. 4 shows the lift mast according to FIG. 1 as seen from the left,

FIG. 5 is a front view of the same lift mast in a retracted position,

FIG. 6 is a cross-sectional view on theline VI-VI in FIG. 5, and

FIG. 7 is a cross-sectional view in an enlarged scale on the lineVII-VII in FIG. 5.

The lift mast comprises three mast sections inserted in each other, anouter 1, an intermediate 2 and an inner 3, of which the outer section 1is secured to the chassis of the truck. A load carriage 4 (FIGS. 2 and3) is movable up and down the inner section 3, said load carriage 4being provided with rulers 5 and 6, which carry forks 7. The loadcarriage 4 includes two columns 17 positioned parallel to and atadistance from each other. These columns 17 are connected by means ofthe rulers 5 and 6.

How the sections are arranged and supported in each other is best shownin F IG. 7, which as a front view and in cross-section discloses theleft uprights of the three sections, and in FIG. 2 and 4.

The outer section 1 consists of two U-shaped, vertical and paralleluprights 8 having their U-openings facing each other. The uprights 8 areplaced at a distance from each other and are connected by means of crossbars'9 and 10.

In the outer section 1 runs the intermediate section 2, which consistsof two vertical and parallel uprights 11, positioned at a distance fromeach other and connected through cross bars 12 and 13. In theintermediate section 2 runs the inner section 3, which consists of twovertical and parallel uprights 14, positioned at a distance from eachother and connected through cross bars 15 and 16.

Each of the two uprights ll of the intermediate section 2 is providedwith a number of guide rolls 18 and 19, arranged in two rows in thelength direction of the uprights, these rolls having for their purposeto guide the three sections 1, 2 and 3 in relation to each other. Theguide rolls 18 and 19 are rotatably mounted about shafts 20, secured tothe uprights ll of the intermediate section 2 and are active between theflanges 21 and i 40 of the U-shaped uprights 8 of the outer section 1and an intermediate flange 22 of the uprights 14 of the inner section 3.

At an unbalance of the mast the sections tend to move in relation toeach other in the axial direction of the rolls l8 and 19. This isprevented thereby that the flanges 21 and 40 of the uprights 8 areprovided with grooves 23, the edges of which work against the two sides25 of the rolls l8 and 19. Furthermore the uprights 14 are provided withshoulders 26 working against the inner sides 25 of the rolls l8 and 19.The less the mast is extended the more rolls will work against the outerand inner sections, which means that the three sections cooperate todecrease the bending of the mast. By inclining the sides 25 of therolls, the edges 24 of the grooves 23 and the shoulders 26 from theradial direction of the rolls, there is ensured a line contact and anideal rolling off.

The movement of the load carriage 4 in the inner section 3 is guided bytwo pairs of rolls 27 (FIG. 3 and 7), an upper pair and a lower pair,which run against a rear flange 29 of the uprights 14, said rolls 28taking the forces which arise when the load carriage 4 is in unbalance.

From the above it is evident that the uprights of the sections to alarge extent are built in into each other and totally they are not widerthan a normal two-stage mast. The cross-sections of the uprights arealso given such dimensions that the material in them all is wellutilized from the point of view of both strength and rigidity. Throughthis redistribution of the material between the uprights included in themast, for a given building length of the mast it is achieved, when themast is retracted, a considerable decrease of the width of the mast,and, when the mast is fully extended, a bending of the mast which isabout half as large as for conventional three-stage masts. Furthermorethe rigidity against bending, when the mast is only partially extended,is further improved as the guide rolls force the uprights of thesections to cooperate. The three-stage masts known before are as a ruleprovided with special rolls for the side guiding, which means that moresurfaces on the uprights of the sections must be machined in relation towhat is necessary at the mast according to the present invention.

The movement upwards of the load carriage 4 is achieved by means of ahydraulic lift cylinder (FIG. 1 and 2), including an outer tube 30, anintermediate tube 31 and a piston-rod 32, and furthermore of anoilsupply pipe 33 with connection nipple 34 and a chain arrangementincluding two lift chains 35. The lift cylinder is of the free liftcylinder type and is positioned bewteen the lower cross bar 12 of theintermediate section 2 and the upper cross bar 16 of the inner section3. The oil supply pipe 33 is secured to the lower cross bar 9 of theouter section 1 and passes via asealing the lower cross bar 12 of theintermediate section 2 and into the tube-shaped piston-rod 32. Thechains 35 with their one ends are secured to the upper cross bar of theouter section 1, run over guide rolls 36 on the lower cross bar 12 ofthe intermediate section 2, over guide rolls 38 on the upper side of themovable outer tube 30 of the hydraulic cylinder and to their othersecuring points in the load carriage 4.

When the oil is pressed into the lift cylinder the movable outer tube 30is first lifted from its lower to its upper position, the load carriage4 thereby, due to the transmission ratio being lifted the doubledistance or to its upper position in the inner section 3. After that thecylinder begins to press the intermediate section 2 and the innersection 3 apart and at the same time the intermediate section 2 islifted due to the securing of the chains to the outer section 1. Theintermediate section 2 is lifted as much in the outer section 1 as theinner section 3 is lifted in the intermediate section 2. During thispart of the lift the load carriage 4 is unmovable in its upper positionin the inner section 3 at the same time as this is lifted at a doublespeed in relation to the speed at which the intermediate section 2 islifted in relation to the unmovable outer section 1. During a loweringoperation of the mast the function is reversed, ie when oil is leavingthe lift cylinder the sections are lowered, after which also the loadcarriage is lowered in relation to the inner section 3.

Having described my invention, 1 claim:

1. A lift truck having a three-stage lift mast comprising:

an outer mast section, an intermediate mast section and an inner mastsection, with said intermediate and said inner section beingtelescopically displaceable lengthwise within said outer section; eachof said mast sections including a pair of upright members horizontallyspaced apart with each member having a base section and a pair offlanges extending from one side of said base section forming said memberin a U-shaped configuration, with the flanges of one of the members ofeach of each pair of members facing toward the other member of saidpair;

a third flange extending from the base section of each of said uprightmembers of said inner mast section on the side thereof opposite the sidefrom which said pair of flanges extend;

means securing said outer section to said lift truck;

a load carriage mounted on said inner section; and

a first and a second vertical row of guide rolls with at least two rollsin each of said rows, said rolls having running surfaces and each beingrotatably mounted upon said base section of said intermediate mastsection positioned in the same vertical plane;

the running surfaces of the rolls of said first row being outwardly inengagement with the inner side of one flange of said outer sectionupright members;

the running surfaces of the rolls of said second row being outwardly inengagement with the inner side of the other of said flanges'of saidouter section upright members;

the running surfaces of the rolls of both said first and said second rowbeing simultaneously inwardly in engagement with one side, respectively,of said third flange of said inner sections, with said third flange ofsaid inner sections being located between said rows of guide rolls;

whereby horizontal extension of said mast perpendicular to the drivedirection of said truck is minimized.

2. A lift truck according to claim 1 wherein the inner sides of bothsaid flanges of said upright members of said outer sections, and whereineach side of said third flange of said upright members of said innersections, are provided with shoulders located for cooperative engagementwith the sides of said rolls.

1. A lift truck having a three-stage lift mast comprising: an outer mastsection, an intermediate mast section and an inner mast section, withsaid intermediate and said inner section being telescopicallydisplaceable lengthwise within said outer section; each of said mastsections including a pair of upright members horizontally spaced apartwith each member having a base section and a pair of flanges extendingfrom one side of said base section forming said member in a U-shapedconfiguration, with the flanges of one of the members of each of eachpair of members facing toward the other member of said pair; a thirdflange extending from the base section of each of said upright membersof said inner mast section on the side thereof opposite the side fromwhich said pair of flanges extend; means securing said outer section tosaid lift truck; a load carriage mounted on said inner section; and afirst and a second vertical row of guide rolls with at least two rollsin each of said rows, said rolls having running surfaces and each beingrotatably mounted upon said base section of said intermediate mastsection positioned in the same vertical plane; the running surfaces ofthe rolls of said first row being outwardly in engagement with the innerside of one flange of said outer section upright members; the runningsurfaces of the rolls of said second row being outwardly in engagementwith the inner side of the other of said flanges of said outer sectionupright members; the running surfaces of the rolls of both said firstand said second row being simultaneously inwardly in engagement with oneside, respectively, of said third flange of said inner sections, withsaid third flange of said inner sections being located between said rowsof guide rolls; whereby horizontal extension of said mast perpendicularto the drive direction of said truck is minimized.
 2. A lift truckaccording to claim 1 wherein the inner sides of both said flanges ofsaid upright members of said outer sections, and wherein each side ofsaid third flange of said upright members of said inner sections, areprovided with shoulders located for cooperative engagemEnt with thesides of said rolls.